<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Radio Interface</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REL="HOME"
TITLE="Video for Linux Two API Specification"
HREF="book1.htm"><LINK
REL="UP"
TITLE="Interfaces"
HREF="c6488.htm"><LINK
REL="PREVIOUS"
TITLE="Teletext Interface"
HREF="x7561.htm"><LINK
REL="NEXT"
TITLE="RDS Interface"
HREF="x7607.htm"></HEAD
><BODY
CLASS="SECTION"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Video for Linux Two API Specification: Revision 0.24</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="x7561.htm"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 4. Interfaces</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x7607.htm"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECTION"
><H1
CLASS="SECTION"
><A
NAME="RADIO"
>4.10. Radio Interface</A
></H1
><P
>This interface is intended for AM and FM (analog) radio
receivers.</P
><P
>Conventionally V4L2 radio devices are accessed through
character device special files named <TT
CLASS="FILENAME"
>/dev/radio</TT
>
and <TT
CLASS="FILENAME"
>/dev/radio0</TT
> to
<TT
CLASS="FILENAME"
>/dev/radio63</TT
> with major number 81 and minor
numbers 64 to 127.</P
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN7585"
>4.10.1. Querying Capabilities</A
></H2
><P
>Devices supporting the radio interface set the
<CODE
CLASS="CONSTANT"
>V4L2_CAP_RADIO</CODE
> and
<CODE
CLASS="CONSTANT"
>V4L2_CAP_TUNER</CODE
> flag in the
<CODE
CLASS="STRUCTFIELD"
>capabilities</CODE
> field of struct&nbsp;<A
HREF="r13105.htm#V4L2-CAPABILITY"
>v4l2_capability</A
>
returned by the <A
HREF="r13105.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_QUERYCAP</CODE
></A
> ioctl. Other combinations of
capability flags are reserved for future extensions.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN7594"
>4.10.2. Supplemental Functions</A
></H2
><P
>Radio devices can support <A
HREF="x542.htm"
>controls</A
>, and must support the <A
HREF="x394.htm"
>tuner</A
> ioctls.</P
><P
>They do not support the video input or output, audio input
or output, video standard, cropping and scaling, compression and
streaming parameter, or overlay ioctls. All other ioctls and I/O
methods are reserved for future extensions.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN7600"
>4.10.3. Programming</A
></H2
><P
>Radio devices may have a couple audio controls (as discussed
in <A
HREF="x542.htm"
>Section 1.8</A
>) such as a volume control, possibly custom
controls. Further all radio devices have one tuner (these are
discussed in <A
HREF="x394.htm"
>Section 1.6</A
>) with index number zero to select
the radio frequency and to determine if a monaural or FM stereo
program is received. Drivers switch automatically between AM and FM
depending on the selected frequency. The <A
HREF="r12342.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_G_TUNER</CODE
></A
> ioctl
reports the supported frequency range.</P
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="x7561.htm"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="book1.htm"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="x7607.htm"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Teletext Interface</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c6488.htm"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>RDS Interface</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
